1. Field of the Invention
This invention relates generally to air operated earth drilling tools, and more particularly to rotary air motor operated earth drills.
2. Brief Description of the Prior Art
The prior art shows a number of examples of air motors used in earth drilling.
Van Huisen U.S. Pat. No. 3,899,033 discloses a pneumatic-kinetic drilling system which relies on the weight and reciprocation of the drill string to drive a piston-cylinder combination to compress air. The compressed air is in turn used to rotate and hammer the drill bit. There is no use of a circulating sub in his patent.
Lyons et al. U.S. Pat. No. 4,432,423 discloses apparatus for extended straight line drilling from a curved borehole.
Lyons U.S. Pat. No. 4,553,611 discloses a pressure drop regulator for downhole turbines.
Schellstede U.S. Pat. No. 4,640,362 discloses a penetration apparatus and method for perforating casing with a high pressure fluid driven punch.
Fox U.S. Pat. No. 4,019,592 discloses a by-pass tool which prevents flow of fluid to all drill string components located below the tool when activated. There is no suggestion to flow all the air through the annulus formed from the outer housing and inner motor/gear box to the drill bit to improve hole cleaning. This tool achieves closure of the by-pass with little or no downward force using opposing seal diameters.
Whittle U.S. Pat. No. 2,865,602 discloses a hydraulic turbine with a by-pass valve integral with the motor. The by-pass is closed when the bit is brought into contact with the bottom of the hole. This brings the telescopic bit stem up against a set of abutments which pushes the sleeve connected to the bit into its upper position causing the mud to pass through the turbine blading. On lifting the drill string off bottom the sleeve is pulled into its lower position by the combined action of gravity and pressure drop across the bit openings. The openings are no longer in register which causes the flow of mud to by-pass the turbine blading.
Gianelloni U.S. Pat. No. 3,194,325 discloses a control valve for turbodrills which provides a means for conducting all the mud supplied to the body to the drill bit while only a portion passes through the turbine for driving the bit. This uses bit weight to close the valve and removal or bit weight to activate the by-pass feature. This patent has a valve and valve seat structure which makes a metal to metal contact when sufficient weight is applied to the drill bit. The weight of the drill is carried through a compression spring. This design of valve is not very effective (ease of opening or closing) in horizontal holes or when air is used as the drilling fluid due to the loss in pump open force and gravity vector.
Lyons U.S. Pat. No. 4,678,045 discloses a turbine tool which includes a method of routing air around the outer diameter of the planetary gear reduction to the drill bit when the motor is operating and enables spent power fluid to be used as drilling fluid and has a bit sub connected to the output shaft of the last stage of gear reduction and supported from the end of the housing which is opposed to the turbine motor.
The present invention is distinguished over the prior art in general, and these patents in particular by a new and improved air motor operated rotary earth drilling tool having a circulation control for inlet air, a rotary air motor, a planetary reduction gear, and a bearing pack connected in series, air from the motor passing over the reduction gear for cooling and through the bearing pack for cooling and discharge into the borehole.